Two-Pipe Steam Radiator - Installation Guide | Castrads
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Two-Pipe Steam Radiator

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Installing a radiator on a two-pipe steam system

Installing a radiator on a two-pipe steam system


Components of a two-pipe steam radiator

Know your system

Before you attempt to replace a two-pipe steam radiator, be certain of what's there already. We highly recommend using a professional, experienced steam engineer. Here are some we know personally and here is the excellent Heating Help database of steam experts across America.

A few things to verify:

  • Is your two-pipe system a true two-pipe, or is it a two-pipe air vent system?
  • Do you have innocuous looking elbows on the return side of your radiators and 'Richardson' branded valves on the inlet? Think twice before removing those elbows!
  • Live in a bigger apartment building? Check with the super whether there's a vacuum pump on the system.

Our best advice is to use an experienced steam specialist - it's not the same skill set as a general plumbing contractor.

Pipe sizing

We supply two-pipe steam radiators with either ½" or ¾ " bushings. Advise us when ordering which size you'll be using.

Site preparation

Ensure the floor surface is well maintained. Don't install a cast iron radiator on unsound flooring.

There is likely to be some residual water inside the radiator from the manufacturing process. This will stain floors, so be sure to protect the area in which you're working.

Cast iron radiators are very heavy. Always protect the floor from scratches.

Know the wall material and measure for wall stays before the radiator is installed - it will make installation much easier. See our wall stay installation guide for more.


If installing the valves BOE (see below), it's important to pitch the radiator by at least 1/16" for every eight sections of radiator.

If installing with the supply at the top then the radiator should be installed level.

Inlet at top: Doesn't require pitch

Inlet at bottom: Requires pitch toward outlet side

Valve installation

Use an adjustable wrench on the valve, or protect surface with a rag. Never use pipe wrench directly on finished surface of the valve - it will damage the decorative finish.

Use a spud wrench to insert spud. Apply sealant such as Teflon tape to the spuds. None is required on the union between the valve and tail nut - the EPDM gasket provides the seal.

Don't connect valve until wall stays installed (if using).

Vacuum breaker

We supply all steam radiators with a vacuum breaker as standard. In certain situations - for instance on a vacuum-pumped system - this may prove problematic. Let us know at the point of ordering if the system operates under vacuum conditions. If the radiator has already arrived with a vacuum breaker, swap it for a plug. The plugs can be switched using a 13mm Allen key.

Post installation

We recommend a boiler service following installation of any new radiator.

cast iron radiator in bathroom with great and white sink and two taps. Mirror.
Mercury 4 Column 34in two-pipe steam radiator in Pewter.


  • Air vent spitting water

Check the pipe sizing is correct
Try altering the boiler pressure
Check the radiator is pitched correctly
Ensure the valve is fully open

  • Radiator not getting hot

Ensure the valve is open
Is the TRV turned down too low?